Steel slag tailing iron recovery process based on dry magnetic separation

Abstract

The invention provides a steel slag tailing iron recovery process based on dry magnetic separation, relates to the technical field of steel slag tailing magnetic separation recovery, and aims to solve the problems of complex iron phase, low waste heat utilization efficiency and the like in steel slag tailings. With deep iron extraction and whole resource circulation as the core, raw material pretreatment targeting strengthening (ultrafine crushing and auxiliary reducing agent precise regulation and control), gradient roasting coupling waste heat cooling reduction (temperature-divided-section adaptation iron phase conversion), multistage magnetic separation and acid leaching combined nano magnetic seed trapping (micro-nano iron recovery) are performed; by matching with a waste heat closed-loop system (smoke generates steam for preheating, power generation and water circulation), the total iron recovery rate is larger than or equal to 88%, energy consumption is reduced by 30-35%, dust is smaller than or equal to 5 mg / m, pickling waste liquid and tailings are fully utilized, the bottleneck that an existing process is low in recovery rate, high in energy consumption and large in environmental protection pressure is broken through, and the recycling requirement of solid waste difficult to treat is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel slag tailings magnetic separation recovery, in particular to a steel slag tailings iron recovery process based on dry magnetic separation. BACKGROUND

[0002] As one of the largest industrial solid wastes in the steel smelting process (annual emissions exceed 100 million tons), the total iron grade of steel slag tailings is usually 18-25%, but the iron resources are mostly in the form of weakly magnetic iron oxide (such as Fe2O3, FeO(OH)) and Fe2O3・SiO2 solid solution that is difficult to dissociate. The magnetic rate of such weakly magnetic iron phase is generally lower than 30%, which cannot be effectively captured by conventional magnetic separation equipment, resulting in about 40-50% of iron resources being wasted with tailings - causing "resource loss" of steel enterprises, and causing serious environmental management problems due to land occupation and leachate pollution of soil and groundwater.

[0003] The current steel slag tailings iron extraction process in the industry is mainly divided into two categories, but its technical drawbacks have become the core bottleneck restricting industrial application: I. Wet magnetic separation process: double constraints of resource consumption and environmental pressure Although wet magnetic separation can improve the iron recovery rate to 75-80% through "water medium dispersion + high gradient magnetic field", it has three fatal defects: Strong dependence on water resources, poor regional applicability: 2.5-3.0 m³ of fresh water is needed per ton of tailings, which faces the dilemma of "no water available" in arid and semi-arid areas in the north; and in winter, the process pipeline and equipment are prone to freeze in low temperature environment, resulting in a reduction in the annual effective production time to 8-10 months, which seriously affects the production continuity; High cost of wastewater treatment, and high environmental protection risk: the wastewater produced after magnetic separation contains a large amount of suspended solids (SS≥500 mg / L) and heavy metal ions (such as Cr, Pb), which requires additional coagulation, sedimentation, and filtration equipment for treatment, with a cost of 8-12 yuan per ton of wastewater, accounting for 15-20% of the total cost of the production line; if the treatment does not meet the emission standards, environmental penalties will also be faced; High energy consumption for subsequent drying, poor economic efficiency: the moisture content of the magnetic separation concentrate is usually 20-25%, which needs to consume additional electric energy or steam to dry to a moisture content of ≤8%, with an increase of 50-80 kW・h of energy consumption per ton of concentrate, further compressing the profit space of enterprises.

[0004] II. Existing dry magnetic separation process: low efficiency of iron extraction and energy utilization In order to avoid the water resource problem of the wet process, the existing dry magnetic separation process has emerged, but the technical shortcomings are more prominent: Low iron recovery rate, unable to meet the industrial demand: Limited by the processing mode of "fixed magnetic field (≤2.0T) + simple crushing", the material dispersion is poor (the proportion of particles of -0.074mm is only 40-50%), the weak magnetic iron phase is not fully dissociated, the iron recovery rate is generally lower than 65%, and the iron concentrate grade is only 45-55%, which is difficult to meet the requirements of blast furnace ironmaking on iron concentrate "grade ≥60%, SiO2≤3%"; Poor adaptability of reduction roasting, serious energy waste: The existing reduction process mostly adopts the mode of "single temperature (750-800℃) + pure electric energy heating" - which cannot match the differentiated needs of Fe2O3 (which needs 700-750℃ reduction), FeO(OH) (which needs to be decomposed at 650-700℃ first), Fe2O3・SiO2 (which needs to break the Si-O bond at 800-850℃), resulting in a weak magnetic iron conversion rate of only 80-85%; and the electric energy consumption accounts for 70-80% of the total energy consumption of the process; Low degree of tailings resource utilization, serious secondary waste: The tailings after magnetic separation (iron grade of 8-12%) are mostly simply used as roadbed fillers or directly stored, without further recovery of the micro-nano iron (particle size <1μm), Fe2SiO4 and other refractory iron phases remaining in the tailings, and without developing high-value utilization paths, causing secondary resource waste, which is inconsistent with the policy guidance of national solid waste full utilization.

[0005] In summary, the existing process is either limited by water resources and region, or trapped in low efficiency and high energy consumption, and cannot achieve the coordinated goals of high recovery rate, low energy consumption, environmental protection and full resource utilization. Therefore, developing a dry magnetic separation process that can adapt to different iron phase tailings, break through the bottleneck of weak magnetic iron recovery, efficiently utilize energy and realize full resource utilization of tailings has become a key technical problem to be solved in the field of solid waste resource utilization in the steel industry. SUMMARY

[0006] The purpose of the present application is to solve the problems raised in the background art, and a steel slag tailings iron recovery process based on dry magnetic separation is proposed.

[0007] The technical scheme adopted by the present application to solve its technical problems is: A steel slag tailings iron recovery process based on dry magnetic separation, comprising the following steps: S1: raw material pretreatment and targeted reduction reinforcement Steel slag tailings (total iron grade 18-25%, containing Fe2O3, Fe3O4, FeO(OH), Fe2O3・SiO2) with particle size ≤10 mm are first pre-removed from strong magnetic impurities by a 0.8-1.2T permanent magnet separator, and then superfine ground to -0.074 mm accounting for ≥75% by a rod mill-airflow pulverizer combination; mixed according to a mass ratio of steel slag tailings: carbonaceous reducing agent: targeted reducing agent: dispersant = 100:(8-12):(0.5-1.5):(0.2-0.5), the carbonaceous reducing agent is a compound of coal powder with fixed carbon ≥50% and biomass charcoal, the targeted reducing agent is selected from at least two of Na2CO3, CaO, and MnO2, and the dispersant is triethanolamine; mixed uniformly by a double screw mixer combined with a 20-40kHz ultrasonic dispersion device, with a uniformity of ≥96%; S2: Gradient roasting and waste heat coupled targeted reduction The mixed material in S1 is sent into an internal heating rotary kiln, and is sequentially gradient roasted at 650-700°C (heat preservation for 15-20 min to decompose FeO(OH)), 700-750°C (heat preservation for 20-30 min to reduce Fe2O3), and 750-800°C (heat preservation for 10-15 min to break the Fe2O3・SiO2 solid solution); the 450-500°C flue gas from the roasting section is introduced into a targeted reduction reactor and reversely contacted with the material, the temperature of the targeted reduction reactor is maintained at 750-800°C by heat exchange coils, and high-temperature flue gas-low-pressure steam double heat source driven carbon reduction is realized, with a weak magnetic iron conversion rate of ≥96%; the roasting energy is coupled by converter gas (70-80% share) and biomass fuel (20-30% share); S3: Low-temperature drying and cooling and waste heat gradient preheating After roasting, the material in S2 is first introduced into a heat pipe heat exchanger, and is exchanged with 200-250°C waste gas discharged from the targeted reduction section, the material is reduced from 800°C to 400-450°C, and the waste gas is increased to 280-320°C; the heated waste gas is divided into two paths: one path (60-70% share) is used for preheating and drying before raw material grinding (to reduce the water content of the tailings from 15-20% to 8-10%), and the other path (30-40% share) is introduced into a hot blast furnace to assist biomass fuel combustion; the material is then introduced into a nitrogen-protected cooling device (one of a conveying type air cooling bed, a drum type cooler, or a fluidized bed cooler), and is cooled to 45-60°C at a rate of 15-30°C / min, and the sensible heat (temperature 200-250°C) of the material is recovered by the built-in heat exchange pipe during the cooling process, and is used for drying the composite carbon reducing agent, and finally the water content of the material is ≤4%; S4: Multistage dry magnetic separation and purification The cooling material in S3 is first coarsely selected by a 1.8-2.5T drum-type high-intensity magnetic separator, and the coarse selection concentrate is classified by a high-frequency vibrating screen with a size of 100-150 meshes, and the oversize material (particle size >0.074mm) is returned to a rod mill for regrinding, and the undersize material is a primary iron concentrate (grade 65-72%); the coarse selection tailings are finely selected by a 2.5-3.0T flat-type high-gradient magnetic separator, and when the proportion of strong magnetic iron is <55% or the proportion of particles with a particle size <0.045mm is >30% is monitored by a laser particle size instrument combined with a magnetic flux sensor, the magnetic field strength is automatically increased by 0.3-0.5T and the material flow rate is reduced to 0.2-0.3m / s, and the fine selection concentrate is a secondary iron concentrate (grade 58-65%), and the fine selection tailings have an iron grade of 4-8%; S5: Iron extraction by acid leaching of the magnetic separation tailings The fine selection tailings are mixed with steel plant pickling waste liquid (containing H2SO4 (15-20%)) at a liquid-solid ratio of 3-5:1, 0.5-1% H2O2 is added as an oxidizing agent, and the leaching is carried out at 70-80℃, 250-300r / min for 40-60min; NH4HCO3 is added to adjust the pH to 3.5-4.5, and FeCO 3; FeCO3 is calcined for 20-30min using the residual heat (350-400℃) to obtain a tertiary iron concentrate (grade ≥60%); S6: Recovery of residual heat in a closed loop The 820-880℃ flue gas (flue gas volume 18000-22000Nm³ / h) from the gradient calcination section is converted into 1.8MPa, 340℃ superheated steam by a water-tube type residual heat boiler, and the steam is divided into four paths: (1) 45-55% is sent to an acid pickling waste liquid preheater (the waste liquid at room temperature is heated to 65-75℃, saving heating energy by 40-50%); (2) 30-35% is sent to a back pressure steam turbine (power 180-250kW) to generate electricity, and the power supply accounts for 30-40% of the total process energy consumption (700-900kW); (3) 10-15% is used for the dissolution and heating (temperature 80-90℃) of a Na2CO3-CaCO3 mixed agent; (4) 5-10% is used for the recovery and regeneration of ethylenediaminetetraacetic acid (heated to 100-110℃, ethylenediaminetetraacetic acid recovery rate ≥80%); the 95-105℃ condensate water produced after steam heat exchange is all used for hot water leaching preparation of leaching residues, and the water resource recovery rate is ≥92%; the temperature, flow rate and reagent addition amount of each residual heat node are controlled by a PLC system, the energy comprehensive utilization rate is ≥60%, the dust emission is ≤3mg / m³, SO2≤35mg / Nm³, NO X ≤50mg / Nm³.

[0008] Further, the targeted reducing agent in S1 is regulated according to Fe phase, when the proportion of FeO (OH) is greater than 30%, the addition amount of Na2CO3 is 1.2-1.5%, and when the proportion of Fe2O3・SiO2 is greater than 25%, CaO and MnO2 are compounded and added (mass ratio 1:1).

[0009] Further, the undersize of the high-frequency vibrating screen in S4 is removed by wet low-intensity magnetic separation, 0.3-0.5% Na2SiO3 inhibitor is added, and the magnetic field strength is 1.5-2.0T, so that the SiO2 content of the final iron concentrate is ≤1.8%.

[0010] Further, the leaching solution in S5 is first captured by a nano-magnetic seed capture device (magnetic seed particle size 50-100nm, magnetic field strength 0.3-0.5T) to capture micro-nano iron, and then NH4HCO3 is added to adjust the pH to 3.5-4.5, wherein the magnetic seed of the nano-magnetic seed capture device is a surface-modified Fe3O4 nanoparticle (the surface modification process of the nano-magnetic seed is: Fe3O4 nanoparticles are added to 0.5-1% hydroxyapatite solution (liquid-solid ratio 10:1), stirred at 60-70°C and 150-200r / min for 30-40min, and then filtered and dried to obtain magnetic seeds coated with hydroxyapatite, with a particle size of 50-100nm, coated with hydroxyapatite on the surface, and a zeta potential of -30~-40mV), and the magnetic seed dosage is dynamically adjusted according to the content of micro-nano iron in the leaching solution (0.8-1.2g of magnetic seed is added for every 1g of micro-nano iron); the magnetic capture section uses a 0.3-0.5T gradient magnetic field (the magnetic field strength increases linearly from 0.3T to 0.5T along the fluid flow direction), the fluid flow rate is controlled at 0.5-1.0m / s, and the residence time is 8-12s; the magnetic seed-micro-nano iron composite particles formed after magnetic capture are intercepted by a 100-150 mesh filter screen and sent to a magnetic seed regeneration unit; the regeneration unit is first cleaned by 25-40kHz ultrasonic waves (power 500-800W, cleaning time 10-15min) to remove surface-attached iron oxides, and then separated by 3000-5000r / min centrifugation (separation time 8-10min) to obtain regenerated magnetic seeds with a purity of ≥98%, and the separated iron mud is mixed with FeCO3.

[0011] Further, the acid leaching residue (iron grade 1.5-3%, containing Fe2SiO4) in S5 is mixed with sodium carbonate (mass ratio 100:8-12) (the mixing of the leaching residue and sodium carbonate is carried out by using a double-shaft paddle mixer (rotation speed 200-250 r / min), and the uniformity of mixing is greater than or equal to 96%), and after the mixing is completed, the mixture is sent into a vertical roasting furnace driven by residual heat of roasting (the flue gas at a gradient roasting section of 500-550 DEG C is used for heating), and is roasted at 800-850 DEG C for 40-60 min, so that Fe2SiO4 is converted into soluble Na2FeO2; the roasting product is leached with hot water at 80-90 DEG C (the sensible heat at 200-250 DEG C recovered in a cooling section is used for heating) for 30-40 min, and then filtration is carried out to obtain a leaching solution containing FeO2² - , dilute sulfuric acid is added to adjust the pH to 2.5-3.0, and Fe(OH)3 is precipitated and obtained, and then is roasted at 350-400 DEG C (using residual heat of FeCO3 roasting) to be converted into a fourth-grade iron concentrate (grade greater than or equal to 58%).

[0012] Further, 0.3-0.5% zinc dihydrogen phosphate double-layer slow-release agents (inner layer of a reducing agent, outer layer of a passivation agent, diameter 4-6 mm, slow-release rate of the reducing agent 0.15-0.25 g / min, and the passivation agent is released at 400-450 DEG C to avoid early reaction with the reducing agent and failure.

[0013] Further, the nitrogen gas (150-180 DEG C) preheated by residual heat of a roasting section is introduced to prevent oxidation while the double-screw mixer is used in combination with a 20-40 kHz ultrasonic dispersion device for mixing in S1.

[0014] Further, the process is applied to the treatment of converter steel slag tailings, blast furnace dust sludge, vanadium-titanium magnetite tailings and steel slag hot smelting tailings with an iron grade of 15-30%, and is especially suitable for the treatment of difficult-to-treat solid wastes containing Fe2O3・SiO2 solid solution (accounting for 28-40%), superfine particle iron (particle size less than 1 um, accounting for 0.8-1.5%) and Fe2SiO4 (accounting for 5-10%).

[0015] Compared with the prior art, the process has the following beneficial effects: 1. Targeted reduction of iron phase precision control system of gradient roasting cooling nano magnetic seeds: According to the differentiated characteristics of Fe2O3 (which needs to be reduced at 700-750℃), FeO(OH) (which needs to be decomposed at 650-700℃), Fe2O3・SiO2 (which needs to be broken at 800-850℃), a three-stage system of pretreatment regulation-roasting matching-capture bottom is constructed-S1 accurately adds a reducing agent according to the iron phase (such as Fe2O3・SiO2 accounts for more than 25%, use CaO-MnO2 complex), S2 uses gradient temperature to reduce in stages, S5 uses nano magnetic seeds to capture the escaped micro-nano iron, and the conversion rate of weakly magnetic iron is increased from 60-70% to 94-96%; (wherein the crushing accuracy of-0.074mm accounts for more than 75% (15% higher than the conventional dry type), the conversion rate of weakly magnetic iron is more than 94% (9% higher than the conventional dry type), the nano magnetic seed capture micro-nano iron (capture rate more than 95%), and the total iron recovery rate can reach 92.3%, far exceeding the upper limit of the wet process); 2. Energy closed loop design: Constructing a full chain cycle of waste heat-process-resources, breaking through the single utilization limitation; The existing process waste heat utilization is mostly one-way output (such as only power generation or only preheating), which is not deeply coupled with the iron extraction core link and resource circulation, resulting in energy waste and additional consumption. This process forms a closed loop system through multi-node linkage: Energy-iron extraction link closed loop: Steam turbine power generation preferentially supplies high energy consumption links such as superfine crushing and magnetic separation equipment, with power supply accounting for 30-40%, reducing dependence on external power purchase; After power generation, 0.3MPa low pressure steam (133℃) is further used for heat supplement in targeted reduction reactor, avoiding waste of medium temperature waste heat; Energy-water resource closed loop: The 95-105℃ condensate water produced after steam heat exchange is all recycled for hot water leaching of leaching slag to prepare, with water resource recovery rate ≥92%, which not only utilizes condensate water waste heat (avoiding cooling energy consumption), but also reduces fresh water consumption, realizing energy-water resource collaborative saving; Energy-drug recovery closed loop: 5-10% of the superheated steam is heated to 100-110℃, which is used for EDTA (ethylenediaminetetraacetic acid) recovery and regeneration, with EDTA recovery rate ≥80%, avoiding additional cost and organic pollution caused by one-time consumption of drugs, and saving the separate heating energy consumption for drug recovery, forming a virtuous cycle of waste heat-drugs-environmental protection; In summary, by utilizing the gradient roasting of 800℃ flue gas, the targeted reduction of 450-500℃ waste gas, and the sensible heat of 200-250℃ in the cooling section—low-grade waste heat—to precisely match the needs of different iron extraction stages, the 800℃ flue gas generates steam to drive power generation (accounting for 30-40% of electricity supply), the 450-500℃ flue gas maintains targeted reduction, and the 200-250℃ sensible heat heats the pickling waste liquid and hot water leaching. The comprehensive energy utilization rate is ≥60%, and the energy consumption per ton of tailings is reduced from 120kW·h in conventional dry processes to 80kW·h. 3. Extreme water saving: Only a small amount of steel plant pickling waste liquid (liquid-solid ratio 3-5:1) is used in the acid leaching process, and the steam condensate recovery rate is ≥92%. The fresh water consumption per ton of tailings is reduced from 2.5-3.0m³ in the wet process to 0.8m³, completely solving the problem of "waterless iron extraction" in northern regions. 4. Leaching residue with an iron content of ≤1.5% is used for cement admixtures (the 3-day compressive strength of cement meets the standard when the admixture content is 22%), and final residue with an iron content of ≤0.8% is used for lightweight partition boards (compressive strength ≥3.9MPa). The added value of tailings is increased from 10 yuan per ton to 50-80 yuan, realizing a qualitative change from industrial solid waste to building material raw materials. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. The present invention will be further described with reference to the embodiments: Example 1: Treatment of converter steel slag tailings (Fe2O3・SiO2 content 35%, FeO(OH) content 32%) 1. Basic characteristics of raw materials Particle size: ≤10mm Total iron content: 23.5% Iron phase composition: Fe2O3・SiO2 (35%), FeO(OH) (32%), Fe3O4 (18%), Fe2O3 (15%) Initial moisture content: 18% 2. Step-by-step process operation and parameter control S1: Raw material pretreatment and targeted reduction enhancement Pre-magnetic separation: A 1.0T permanent magnet separator is used to remove strongly magnetic Fe3O4 impurities. After pre-magnetic separation, the total iron content of the tailings is reduced to 21.8%, and the removal rate of strongly magnetic impurities is 93%. Ultrafine grinding: rod mill (rotating speed 190 r / min) + jet mill (air pressure 0.9 MPa) in combination, after grinding, sampling detection, -0.074 mm particles accounted for 78%; Material mixing: steel slag tailings: carbonaceous reducing agent: targeted reducing agent: dispersant = 100:10:1.3:0.4 by mass ratio: Carbonaceous reducing agent: coal powder (fixed carbon 56%) + biomass charcoal (fixed carbon 52%) compounded at 1:1 (fixed carbon ≥ 50%); Targeted reducing agent: due to FeO(OH) accounted for 32% (> 30%) and Fe2O3・SiO2 accounted for 35% (> 25%), 1.3% of the mixed agent (1.2% Na2CO3 + 0.6% CaO-MnO2 (1:1 compounded)) was added, and 0.4% of the zinc dihydrogen phosphate double-layer slow-release agent (diameter 5 mm, reducing agent slow-release rate 0.2 g / min) was added; Dispersant: triethanolamine; Mixing and anti-oxidation: through the combination of double screw mixer (rotating speed 320 r / min) + 30 kHz ultrasonic dispersion equipment, the mixing uniformity detection was 97.2% (≥ 96% requirement); at the same time, 165°C preheated nitrogen (150-180°C range) was introduced, and the oxidation rate of the material was <0.8%. S2: gradient roasting and waste heat coupling targeted reduction Gradient roasting: the mixed material was sent into a Φ2.0m×14m internal heating rotary kiln, and was sequentially kept at 680°C for 18 min (to decompose FeO(OH)), 730°C for 25 min (to reduce Fe2O3), and 780°C for 12 min (to break Fe2O3・SiO2 solid solution); Waste heat coupling reduction: the 480°C flue gas (range 450-500°C) from the roasting section was introduced into the targeted reduction reactor and contacted with the material in reverse, the reactor temperature was maintained at 780°C through Φ60mm stainless steel heat exchange coil, and high-temperature flue gas-low-pressure steam double heat source driving was realized; Energy configuration: the roasting energy used 75% converter gas + 25% biomass fuel, and the biomass fuel was wood pellet (heat value 18 MJ / kg); Reduction effect: sampling detection showed that the weak magnetic iron conversion rate was 96.5% (≥ 96% requirement), and the Fe2O3・SiO2 solid solution breakage rate was 98.2%. S3: low-temperature drying and cooling and waste heat gradient preheating Waste heat exchange: after roasting, the 800°C material entered the heat pipe heat exchanger and exchanged heat with the 230°C exhaust gas discharged from the targeted reduction section, the material was cooled to 430°C, and the exhaust gas was heated to 305°C; Exhaust gas reuse: the 305℃ exhaust gas after heating is divided into two parts: ①70% is used to preheat the raw material before crushing, reducing the moisture content of the tailings from 18% to 9%; ②30% is sent to the hot blast stove to assist the combustion of biomass fuel, saving 25% of biomass fuel consumption; Cooling control: the material is sent to a drum cooler under nitrogen protection (rotation speed 0.8r / min), the cooling rate is 20℃ / min, and the temperature after cooling is 55℃; during the cooling process, 230℃ sensible heat is recovered through the built-in heat exchange pipe and used for drying the carbonaceous reducing agent (reducing the moisture content of the reducing agent from 12% to 4%), and the final moisture content of the material is detected as 3.8% (≤4% requirement). S4: multi-stage dry magnetic separation and purification Coarse separation: a 2.2T drum-type high-intensity magnetic separator is used, the drum rotation speed is 1.2m / s, and the coarse concentrate has a total iron grade of 68.5%; Classification and regrinding: the coarse concentrate passes through a 120-mesh high-frequency vibrating screen, the oversize material (particle size >0.074mm, accounting for 11%) is returned to the rod mill for regrinding, and after regrinding, the -0.074mm fraction accounts for 92%; Wet impurity removal: according to claim 3, the undersize material is added with 0.4% Na2SiO3 inhibitor, a 1.8T wet low-intensity magnetic separator is used for impurity removal, and a primary iron concentrate is obtained, with a total iron grade of 71.8% and a SiO2 content of 1.6% (≤1.8% requirement); Cleaning: the coarse tailings (total iron grade 7.2%) are treated with a 2.8T flat-type high-gradient magnetic separator, the laser particle size analyzer + magnetic flux sensor monitoring shows that the strongly magnetic iron accounts for 53% and the particle size <0.045mm accounts for 32%, the magnetic field strength is automatically increased to 3.3T and the material flow rate is reduced to 0.25m / s, the cleaning concentrate has a total iron grade of 63.2%, and the cleaning tailings have a total iron grade of 5.5%. S5: acid leaching of magnetic separation tailings Acid leaching operation: the cleaning tailings (total iron grade 5.5%) are mixed with 17% steel plant acid pickling waste liquid at a liquid-solid ratio of 4:1, 0.8% H2O2 is added, and leaching is carried out at 75℃, 280r / min for 50min; Nanometer magnetic seed capture: according to claim 4, the leaching solution is first passed through a nanometer magnetic seed capture device: Magnetic seed preparation: Fe3O4 nanoparticles are added to 0.8% calcium hydroxyl phosphate solution (liquid-solid ratio 10:1), stirred at 65℃, 180r / min for 35min, filtered and dried to obtain magnetic seeds coated with calcium hydroxyl phosphate (particle size 85nm, zeta potential -36mV); Trapping parameters: micro-nano iron content in leaching solution 1.2 g / L, 1.0 g magnetic seeds / g micro-nano iron was added, 0.3-0.5T gradient magnetic field (0.3T at inlet, 0.5T at outlet) was used, fluid flow rate 0.8 m / s, residence time 10 s, 120 mesh filter screen was used to intercept composite particles; Magnetic seed regeneration: the composite particles were cleaned by 35 kHz ultrasonic wave (power 700 W, time 12 min), and centrifuged at 4000 r / min for 9 min, to obtain regenerated magnetic seeds with purity 98.5% and recovery rate 96.2%, and the mixture of iron mud and FeCO3 was separated; Precipitation and roasting: NH4HCO2 was added to the leaching solution to adjust the pH to 4.0, FeCO3 was obtained by precipitation, and the third grade iron concentrate was obtained by roasting at 380℃ for 25 min using the waste heat, and the total iron grade was 61.5% (≥60% required). S6: waste heat closed loop recovery Steam preparation: the 850℃ flue gas (20000 Nm³ / h) from the gradient roasting section was introduced into the water-tube waste heat boiler to produce 1.8 MPa, 340℃ superheated steam 9.5 t / h; Steam distribution: 52% (4.94 t / h, 45-55% range) was sent to the pickling waste liquid preheater to heat the 25℃ waste liquid to 70℃, saving heating energy by 47%); 32% (3.04 t / h, 30-35% range) was sent to the 220 kW back pressure steam turbine, the power generation was 205 kW, accounting for 25% of the total process energy consumption 820 kW (because the Fe2O3・SiO2 ratio was high, the energy consumption was slightly higher); 12% (1.14 t / h, 10-15% range) was used for dissolving and heating the Na2CO3-CaCO3 mixed agent, and the temperature was maintained at 85℃; 4% (0.38 t / h, 5-10% range lower limit, because the amount of EDTA was small) was used for ethylenediaminetetraacetic acid recovery and regeneration, and heated to 108℃, the EDTA recovery rate was 83% (≥80% required); Water resource recycling: 98℃ condensate water was produced after steam heat exchange, the recovery rate was 93.5% (≥92% required), and it was all used for hot water leaching of leaching residue; Environmental protection index: PLC system linkage control, dust emission 2.8 mg / m³ (≤3 mg / m³ required), SO2 31 mg / Nm³ (≤35 mg / Nm³ required), NO X 45 mg / Nm³ (≤50 mg / Nm³ required), energy comprehensive utilization rate 62.3% (≥60% required). S7: deep iron extraction from acid leaching residue Mixing and roasting: S5 acid leaching residue (total iron grade 1.8%, Fe2SiO4 9%) and sodium carbonate were mixed at 100:10, using a double-shaft paddle mixer (speed 230 r / min), and the mixing uniformity was detected as 97% (≥96% required); the mixture was fed into a vertical roaster (using 530℃ flue gas from the gradient roasting section for heating), and roasting was carried out at 830℃ for 50 min; Hot water leaching and precipitation: the roasting product was leached with 85℃ hot water (using 230℃ sensible heat from the S3 cooling section for heating) for 35 min, and FeO2 2- Leaching solution; dilute sulfuric acid was added to adjust the pH to 2.8, and Fe(OH)3 was precipitated, and the residual heat of FeCO3 roasting was used for roasting at 380℃, to obtain a fourth-stage iron concentrate with a total iron grade of 59.2% (≥58% required). 3. Key results of Example 1 Total iron recovery rate: 92.8% Total yield of iron concentrate: 22.3% (first-stage 71.8% + second-stage 63.2% + third-stage 61.5% + fourth-stage 59.2%) Final tailings iron grade: 0.7% Energy comprehensive utilization rate: 62.3% Water resource recovery rate: 93.5% Example 2 Processing blast furnace dust mud (ultra-fine particle iron accounting for 1.4%, FeO(OH) accounting for 35%) 1. Raw material characteristics Particle size: ≤8 mm, total iron grade 24.2% Iron phase: ultra-fine particle iron (particle size <1 μm, 1.4%), FeO(OH) (35%), Fe2O3 (40%), Fe3O4 (13.6%) Initial moisture content: 16% 2. Core adjustment and results (only difference items from Example 1) S1 targeted reduction aid: due to the FeO(OH) accounting for 35% (>30%), 1.5% Na2CO3 was added, and the mixing uniformity was 96.8%; S5 nano magnetic seed capture: the micro-nano iron content in the leaching solution was 1.6 g / L, the magnetic seed dosage was 1.2 g / g micro-nano iron, the capture rate was 96.8%, and the total iron grade of the third-stage iron concentrate was 63.2%; Key results: total iron recovery rate 93.5%, ultra-fine particle iron recovery rate 95.5%, final tailings iron grade 0.6%, energy comprehensive utilization rate 63.8%. Example 3 Processing steel slag hot decompression tailings (Fe2SiO4 accounting for 9.5%, Fe2O3・SiO2 accounting for 29%) 1. Raw material characteristics Particle size: ≤10 mm, total iron grade 20.5% Iron phase: Fe2SiO4(9.5%), Fe2O3・SiO2(29%), Fe3O4(38%), Fe2O3(23.5%) Initial moisture content: 19% 2. Core adjustment and results (only difference items with example 1) S7 acid leaching slag iron extraction: Fe2SiO4 conversion efficiency 96.1%, four-stage iron concentrate total iron grade 59.8%; Key results: total iron recovery rate 91.2%, Fe2SiO4 recovery rate 93.8%, final tailings iron grade 0.8%, water resource recovery rate 92.8%. The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A dry magnetic separation based process for iron recovery from steel slag tailings, characterized in that, Comprising the following steps: S1: raw material pretreatment and targeted reduction strengthening The steel slag tailings with particle size ≤10 mm (total iron grade 18-25%, containing Fe2O3, Fe3O4, FeO(OH), Fe2O3・SiO2) are first pre-removed from strong magnetic impurities by a 0.8-1.2T permanent magnet separator, and then superfine ground to -0.074mm accounting for ≥75% by a rod mill-airflow pulverizer combination; mixed according to the mass ratio of steel slag tailings: carbonaceous reducing agent: targeted reducing agent: dispersant = 100:(8-12):(0.5-1.5):(0.2-0.5), the carbonaceous reducing agent is a compound of coal powder with fixed carbon ≥50% and biomass charcoal, the targeted reducing agent is selected from at least two of Na2CO3, CaO, MnO2, and the dispersant is triethanolamine; mixed evenly by a double screw mixer combined with a 20-40kHz ultrasonic dispersion device, with a uniformity of ≥96%; S2: gradient roasting and waste heat coupled targeted reduction The mixed material in S1 is sent into an internal heating rotary kiln, and is sequentially gradient roasted at 650-700℃ (heat preservation for 15-20min to decompose FeO(OH)), 700-750℃ (heat preservation for 20-30min to reduce Fe2O3), and 750-800℃ (heat preservation for 10-15min to break the Fe2O3・SiO2 solid solution); the 450-500℃ flue gas from the roasting section is introduced into the targeted reduction reactor and contacted with the material in the opposite direction, the temperature of the targeted reduction reactor is maintained at 750-800℃ by heat exchange coils, realizing carbon reduction driven by high-temperature flue gas and low-pressure steam double heat sources, and the weak magnetic iron conversion rate is ≥96%; the roasting energy is coupled by converter gas (70-80%) and biomass fuel (20-30%); S3: low-temperature drying and cooling and waste heat gradient preheating After roasting, the material in S2 is first introduced into a heat pipe heat exchanger, and is exchanged with 200-250℃ waste gas discharged from the targeted reduction section, the material is reduced from 800℃ to 400-450℃, and the waste gas is heated to 280-320℃; the heated waste gas is divided into two paths: one path (60-70%) is used for preheating and drying before raw material grinding (reducing the water content of the tailings from 15-20% to 8-10%), and the other path (30-40%) is sent into a hot blast furnace to assist biomass fuel combustion; the material is then introduced into a nitrogen-protected cooling device (one of a conveying type air cooling bed, a drum type cooler, or a fluidized bed cooler), and is cooled to 45-60℃ at a rate of 15-30℃ / min, and the sensible heat (temperature 200-250℃) of the material is recovered by the built-in heat exchange pipe during the cooling process, and is used for drying the composite carbon reducing agent, and finally the water content of the material is ≤4%; S4: multi-stage dry magnetic separation and purification The cooling material in S3 is first coarsely selected by a 1.8-2.5T drum-type high-intensity magnetic separator, and the coarse selection concentrate is classified by a high-frequency vibrating screen with a size of 100-150 meshes, the oversize (particle size >0.074mm) is returned to the rod mill for regrinding, and the undersize is the primary iron concentrate (grade 65-72%); the coarse selection tailings are finely selected by a 2.5-3.0T flat plate high gradient magnetic separator, when the proportion of strong magnetic iron is <55% or the proportion of particles with a particle size <0.045mm is >30% is monitored by a laser particle size instrument combined with a magnetic flux sensor, the magnetic field strength is automatically increased by 0.3-0.5T and the material flow rate is reduced to 0.2-0.3m / s, and the fine selection concentrate is the secondary iron concentrate (grade 58-65%), and the fine selection tailings have an iron grade of 4-8%; S5: Iron extraction by acid leaching of magnetic separation tailings The selected tailings are mixed with pickling waste liquid (containing H2SO4 (15-20%)) of a steel plant at a liquid-solid ratio of 3-5:1, 0.5-1% H2O2 is added as an oxidizing agent, and leaching is carried out at 70-80℃ and 250-300r / min for 40-60min; then NH4HCO3 is added to adjust the pH to 3.5-4.5, and FeCO 3; FeCO3 is roasted by using the waste heat (350-400℃) for 20-30min to obtain the third-grade iron concentrate (grade≥60%). S6: Waste heat closed loop recovery The 820-880℃ flue gas (flue gas volume 18000-22000Nm³ / h) in the gradient roasting section is converted into 1.8MPa, 340℃ superheated steam by a water-tube waste heat boiler, and the steam is divided into four paths: (1) 45-55% is sent to an acid pickling waste liquid preheater (waste liquid at room temperature is heated to 65-75℃, saving heating energy by 40-50%); (2) 30-35% is sent to a back pressure steam turbine (power 180-250kW) for power generation, and the power supply accounts for 30-40% of the total process energy consumption (700-900kW); (3) 10-15% is used for the dissolution and heating (temperature 80-90℃) of Na2CO3-CaCO3 mixed agent; (4) 5-10% for the recovery and regeneration of ethylenediaminetetraacetic acid (heated to 100-110°C, ethylenediaminetetraacetic acid recovery rate ≥80%); the 95-105°C condensed water generated after steam heat exchange is all used for hot water leaching preparation of leaching residue, and the water resource recovery rate is ≥92%; the temperature, flow and reagent addition amount of each residual heat node are controlled by the PLC system linkage, the energy comprehensive utilization rate is ≥60%, the dust emission is ≤3mg / m³, SO2 is ≤35mg / Nm³, NO X ≤50mg / Nm³.

2. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, In S1, the targeted reducing agent is adjusted according to the Fe phase, when the proportion of FeO(OH) is >30%, the addition amount of Na2CO3 is 1.2-1.5%, and when the proportion of Fe2O3・SiO2 is >25%, CaO and MnO2 are compounded and added (mass ratio 1:1).

3. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, In S4, the undersize of the high-frequency vibrating screen is removed by wet low-intensity magnetic separation, 0.3-0.5% Na2SiO3 inhibitor is added, the magnetic field strength is 1.5-2.0T, and the final iron concentrate has a SiO2 content of ≤1.8%.

4. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, The leaching solution in S5 is first captured by nano-magnetic seed capturing equipment (magnetic seed particle size 50-100 nm, magnetic field strength 0.3-0.5 T) after the micro-nano iron is captured, and then NH4HCO3 is added to adjust the pH to 3.5-4.5, wherein the magnetic seed of the nano-magnetic seed capturing equipment is a surface modified Fe3O4 nanoparticle (the surface modification process of the nano-magnetic seed is: Fe3O4 nanoparticles are added to 0.5-1% hydroxyapatite solution (liquid-solid ratio 10:1), stirred at 60-70°C, 150-200 r / min for 30-40 min, and then filtered and dried to obtain magnetic seeds coated with hydroxyapatite, with a particle size of 50-100 nm, coated with hydroxyapatite on the surface, and a zeta potential of-30~-40 mV), and the magnetic seed dosage is dynamically adjusted according to the content of micro-nano iron in the leaching solution (0.8-1.2 g of magnetic seed is added per 1 g of micro-nano iron); the magnetic capture section uses a 0.3-0.5 T gradient magnetic field (the magnetic field strength increases linearly from 0.3 T to 0.5 T along the fluid flow direction), and the fluid flow rate is controlled at 0.5-1.0 m / s, with a residence time of 8-12 s; the magnetic seed-micro-nano iron composite particles formed after magnetic capture are intercepted by a 100-150 mesh filter screen and sent to the magnetic seed regeneration unit; the regeneration unit is first cleaned by 25-40 kHz ultrasonic waves (power 500-800 W, cleaning time 10-15 min) to remove surface-attached iron oxides, and then separated by 3000-5000 r / min centrifugation (separation time 8-10 min) to obtain regenerated magnetic seeds with a purity of ≥98%, and the separated iron mud is mixed with FeCO3.

5. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, The acid leaching residue (Fe grade 1.5-3%, containing Fe2SiO4) in S5 is mixed with sodium carbonate (mass ratio 100:8-12) (the mixing of the leaching residue and sodium carbonate is carried out by using a double-shaft paddle mixer (rotation speed 200-250 r / min), and the mixing uniformity is ≥96%), and after the mixing is completed, the mixture is sent into a vertical roasting furnace driven by roasting residual heat (gradient roasting section 500-550℃ flue gas is used for heating), and is roasted at 800-850℃ for 40-60 min, so that Fe2SiO4 is converted into soluble Na2FeO2; the roasting product is leached with 80-90℃ hot water (200-250℃ sensible heat recovered in the cooling section is used for heating) for 30-40 min, and filtration is carried out to obtain a leaching solution containing FeO2² - , dilute sulfuric acid is added to adjust the pH to 2.5-3.0, Fe(OH)3 is precipitated, and is converted into a fourth-stage iron concentrate (grade ≥58%) by roasting at 350-400℃ (roasting residual heat of FeCO3 is used).

6. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, 0.3-0.5% zinc dihydrogen phosphate double-layer slow-release agent (inner layer of reducing agent, outer layer of passivation agent, diameter 4-6 mm, reducing agent release rate 0.15-0.25 g / min, passivation agent releases at 400-450°C to avoid premature reaction with the reducing agent.

7. The dry magnetic separation based process for recovering iron from steel slag tailings according to claim 1, characterized in that, In S1, nitrogen preheated by the waste heat of the roasting section (150-180°C) is introduced to prevent oxidation while mixing by a double-screw mixing machine combined with a 20-40 kHz ultrasonic dispersion device.

8. The process according to any one of claims 1-9 is applied to the treatment of converter steel slag tailings, blast furnace dust slurry, vanadium-titanium magnetite tailings, and steel slag hot decompression tailings with an iron grade of 15-30%, especially for difficult-to-treat solid waste containing Fe2O3・SiO2 solid solution (accounting for 28-40%), ultra-fine particle iron (particle size <1 μm, accounting for 0.8-1.5%), and Fe2SiO4 (accounting for 5-10%).